Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $87.70   11.659%   $97.9249   $97.92   $97.90   $97.90  
  Purchase #2 $87.32   12.562%   $98.2891   $98.29   $98.30   $98.30  
  Purchase #3 $75.77   11.463%   $84.4555   $84.46   $84.45   $84.50  
  Purchase #4 $166.57   8.396%   $180.5552   $180.56   $180.55   $180.60  
  Purchase #5 $90.29   6.491%   $96.1507   $96.15   $96.15   $96.20  
  Purchase #6 $174.90   9.291%   $191.15   $191.15   $191.15   $191.20  
  Purchase #7 $241.70   13.499%   $274.3271   $274.33   $274.35   $274.30  
  7 purchase totals = $924.25       $1,022.8525   $1,022.86   $1,022.85   $1,023.00